Methods of controlling polymer properties

ABSTRACT

The invention generally provides for methods for controlling polymer properties. In particular, invention provides for methods for controlling the comonomer composition distribution of polyolefins such as ethylene alpha-olefin copolymers by altering at least one or more of the following parameters: the molar ratio of hydrogen to ethylene, the molar ratio of comonomer to ethylene, the partial pressure of ethylene, and the reactor temperature without substantially changing the density and/or the melt index of the copolymer.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of Ser. No. 12/523,400,filed Feb. 18, 2010, which claims the benefit of Ser. No. 60/899,526,filed Feb. 5, 2007, the disclosures of which are incorporated byreference in their entireties.

FIELD OF THE INVENTION

The invention generally relates to methods for controlling polymerproperties. In particular, the invention relates to methods forcontrolling the comonomer composition distribution of polyolefins suchas ethylene alpha-olefin copolymers.

BACKGROUND

The composition distribution of a polyolefin such as an ethylenealpha-olefin copolymer refers to the distribution of comonomer (shortchain branches) among the molecules that comprise the polyethylenepolymer. When the amount of short chain branches varies among thepolyethylene molecules, i.e., the amount of comonomer per 1000 carbonsatoms varies with the length of the polyethylene molecules, the resin issaid to have a “broad” composition distribution. When the amount ofcomonomer per 1000 carbons is similar among the polyethylene moleculesof different chain lengths, the composition distribution is said to be“narrow.”

The composition distribution is known to influence the properties ofcopolymers, for example, extractables content, environmental stresscrack resistance, heat sealing, and tear strength. The compositiondistribution of a polyolefin may be readily measured by methods known inthe art, for example, temperature raising elution fractionation (TREF)or crystallization analysis fractionation (CRYSTAF).

Polyolefins such as ethylene alpha-olefin copolymers are typicallyproduced in a low pressure reactor, utilizing, for example, solution,slurry, or gas phase polymerization processes. Polymerization takesplace in the presence of catalyst systems such as those employing, forexample, a Ziegler-Natta catalyst, a chromium based catalyst, ametallocene catalyst, or combinations thereof.

It is generally known in the art that a polyolefin's compositiondistribution is largely dictated by the type of catalyst used andtypically invariable for a given catalyst system. Ziegler-Nattacatalysts and chromium based catalysts produce resins with broadcomposition distributions, whereas metallocene catalysts normallyproduce resins with narrow composition distributions. However, U.S. Pat.No. 6,242,545 and WO 2004/000919 disclose certain metallocenes, such ashafnocenes, that produce polyethylenes having a broad compositiondistribution.

Although the composition distribution is primarily dictated by thecatalyst system used, attempts have been made to change the compositiondistribution of a polyolefin. For example, a desired compositiondistribution may be achieved with polymer blends. U.S. Pat. No.5,382,630 discloses, inter alia, linear ethylene interpolymer blendsmade from components that can have the same molecular weight butdifferent comonomer contents, or the same comonomer contents butdifferent molecular weights, or comonomer contents that increase withmolecular weight.

Another way to change the composition distribution utilizes multiplecatalysts that respond differently to the comonomer concentrationpresent in the reactor as is disclosed in, for example, U.S. PatentApplication Publication Nos. 2004/0225088 and 2004/0122054.

And still other ways to produce a polyolefins having desired compositiondistributions is through the use of multiple reactors with one or morecatalyst systems and/or with the use of a condensable agent in thereactor. For example, WO2006/007046 discloses, inter alia, a method ofbroadening the composition distribution breadth index (CDBI) of a singlereactor/single catalyst system by increasing the amount of condensableagent in the reactor. However, sometimes there is no condensable agentpresent in the reactor or increasing the amount of condensable agent isnot feasible because doing so would introduce particle stickiness and/oroperability problems.

Other background references include WO 01/49751, WO 01/98409, EP 1 669373 A, and U.S. Patent Application Publication Nos. 2004/121922 and2005/148742.

Thus, methods to control the composition distribution of a polyolefin,such as an ethylene alpha-olefin copolymer, without having to use mixedcatalysts, multiple reactors, condensable agents, and/or post reactorblending would be desirable and advantageous.

SUMMARY

The inventors have discovered such methods where the compositiondistribution of a polyolefin such as an ethylene alpha-olefin copolymermay be adjusted by altering at least one or more of the following: themolar ratio of hydrogen to ethylene, the molar ratio of comonomer toethylene, the partial pressure of ethylene, and the reactor temperature.

The change or altering in composition distribution may be characterizedby at least one or more of the following:

-   -   a) the composition distribution changes such that the T₇₅-T₂₅        value changes by at least 5° C. or the T₉₀ value changes by at        least 5° C. (as herein defined);    -   b) the area under the high temperature peak in a TREF or CRYSTAF        experiment (as herein defined) increases or decreases by at        least 5%;    -   c) the fraction of non-crystallizing polymer chains changes by        at least 5%, wherein the fraction of non-crystallizing polymer        chains is indicated by a stepwise increase in the trace below        30° C. in a CRYSTAF experiment (as herein defined);    -   d) a decrease of one peak in a TREF or a CRYSTAF experiment (as        herein defined) of a polyethylene having a bimodal composition        distribution changes such that a unimodal composition        distribution results; and    -   e) the appearance of an additional peak in a TREF or a CRYSTAF        experiment (as herein defined) of a polyethylene having a        unimodal composition distribution changes such that a bimodal        composition distribution results.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a representation of the TREF curves from examples 1-4 fromTable 1, plotting normalized concentration as a function of elutiontemperature.

FIG. 2 is a representation of the TREF curves from examples 5-8 fromTable 2, plotting normalized concentration as a function of elutiontemperature.

FIG. 3 is a representation of the CRYSTAF curves from examples 12 and 13from Table 3, plotting the derivative of the cumulative concentrationcurve as a function of the crystallization temperature.

FIG. 4 is a representation of the CRYSTAF curves from examples 11 and 12from Table 3, plotting the derivative of the cumulative concentrationcurve as a function of the crystallization temperature.

FIG. 5 is a representation of the CRYSTAF curves from examples 9 and 10from Table 3, plotting the derivative of the cumulative concentrationcurve as a function of the crystallization temperature.

DETAILED DESCRIPTION

Before the present compounds, components, compositions, and/or methodsare disclosed and described, it is to be understood that unlessotherwise indicated this invention is not limited to specific compounds,components, compositions, reactants, reaction conditions, ligands,metallocene structures, or the like, as such may vary, unless otherwisespecified. It is also to be understood that the terminology used hereinis for the purpose of describing particular embodiments only and is notintended to be limiting.

It must also be noted that, as used in the specification and theappended claims, the singular forms “a,” “an” and “the” include pluralreferents unless otherwise specified. Thus, for example, reference to “aleaving group” as in a moiety “substituted with a leaving group”includes more than one leaving group, such that the moiety may besubstituted with two or more such groups. Similarly, reference to “ahalogen atom” as in a moiety “substituted with a halogen atom” includesmore than one halogen atom, such that the moiety may be substituted withtwo or more halogen atoms, reference to “a substituent” includes one ormore substituents, reference to “a ligand” includes one or more ligands,and the like.

Embodiments of the invention are directed to methods for controlling thecomposition distribution of polyolefins such as ethylene alpha-olefincopolymers by altering at least one or more of the following: the molarratio of hydrogen to ethylene, the molar ratio of comonomer to ethylene,the reactor temperature, and the partial pressure of ethylene, in areactor.

In another class of embodiments, the invention is directed to a methodfor changing the composition distribution of an ethylene alpha-olefincopolymer having of a bimodal composition distribution such that theratio of the high temperature peak to low temperature peak in a CRYSTAFor a TREF experiment changes by at least 10%. Such results may beaccomplished by altering at least one or more of the following: themolar ratio of hydrogen to ethylene, the molar ratio of comonomer toethylene, the partial pressure of ethylene, and the reactor temperature,in a reactor, optionally, without substantially changing the copolymer'sdensity.

In yet another class of embodiments, the invention is directed to amethod for changing the composition distribution of an ethylenealpha-olefin copolymer having of a bimodal composition distribution suchthat the ratio of the high temperature peak to low temperature peak in aCRYSTAF or a TREF experiment changes by at least 10%. This may beaccomplished by altering at least one or more of the following: themolar ratio of hydrogen to ethylene, the molar ratio of comonomer toethylene, the partial pressure of ethylene, and the reactor temperature,optionally, without substantially changing the copolymer's density ormelt index.

In a class of embodiments, the invention is directed to a method ofchanging the composition distribution of an ethylene alpha-olefincopolymer wherein the change in composition distribution ischaracterized by a change in the T₇₅-T₂₅ value by 5° C. or more. Thismay be accomplished by altering at least one or more of the following:the molar ratio of hydrogen to ethylene, the molar ratio of comonomer toethylene, the partial pressure of ethylene, and the reactor temperature,optionally, without substantially changing the copolymer's density ormelt index.

In another class of embodiments, the invention is directed to a methodof changing the composition distribution of an ethylene alpha-olefincopolymer wherein the change in composition distribution ischaracterized by a change in the T₉₀ value by 5° C. or more. This may beaccomplished by altering one or more of the following: the molar ratioof hydrogen to ethylene, the molar ratio of comonomer to ethylene, thepartial pressure of ethylene, and the reactor temperature, optionally,without substantially changing the copolymer's density or melt index.

In another class of embodiments, the invention is directed to a methodof forming a first and a second ethylene alpha-olefin copolymer, themethod comprising contacting a single catalyst system, ethylene, atleast one alpha-olefin other than ethylene, under polymerizableconditions in a single reactor;

wherein the first and a second ethylene alpha-olefin copolymer both havea density of 0.910 g/cc or greater, a melt index ratio from 15 to 50,and polymerized in a single reactor using single catalyst, and

(a) wherein said first ethylene alpha-olefin copolymer is characterizedby a monomodal composition distribution characterized as having a singlepeak in a TREF experiment, and

wherein said second ethylene alpha-olefin copolymer has a multimodalcomposition distribution characterized as having at least two peaks in aTREF experiment; or,

(b) wherein said first ethylene alpha-olefin copolymer has a multimodalcomposition distribution characterized by having at least two peaks in aTREF experiment, and

said second ethylene alpha-olefin copolymer has a monomodal compositiondistribution characterized by having a single peak in a TREF experiment.

Also disclosed herein is a method of forming a first and a secondethylene alpha-olefin copolymer, the method comprising contacting areaction mixture and a catalyst system comprising a hafnocene in areactor, the reaction mixture comprising ethylene, hydrogen, and one ormore alpha olefins, and altering at least one or more of the following:i) the molar ratio of hydrogen to ethylene, ii) the molar ratio ofcomonomer to ethylene, iii) the ethylene partial pressure and, and iv)the reactor temperature; so that the first ethylene alpha-olefincopolymer has a monomodal composition distribution characterized byhaving a single peak in a TREF experiment and the second ethylenealpha-olefin copolymer has a multimodal composition distributioncharacterized by having at least two peaks in a TREF experiment.

DEFINITIONS

As used herein, “polyethylene” refers to at least one ethylenealpha-olefin copolymer, the alpha-olefin being, for example, hexeneand/or butene.

As used herein, “composition distribution” (sometimes referred to andused interchangeably as “comonomer composition distribution” or “shortchain branch distribution”) is the distribution of comonomer among themolecules that comprise the polyethylene resin. The compositiondistribution may be determined by a TREF or CRYSTAF experiment asdescribed herein.

As used herein, a monomodal composition distribution may be identifiedby having only one distinct peak in a TREF or CRYSTAF experiment asdescribed herein. A multimodal composition distribution, sometimes insome embodiments, a bimodal composition distribution, is identified bythe appearance of at least two distinct peaks (e.g., two or more), ahigh temperature peak and a low temperature peak, in a TREF or a CRYSTAFexperiment as described herein. A “peak” is present when the generalslope of the graph changes from positive to negative with increasingtemperature. Two “peaks” are present when there is a local minimumpresent between the peaks in which the general slope of the graphchanges from negative to positive with increasing temperature. Therelative ratio of the two peaks may be determined from a TREF or CRYSTAFcurve using a Gaussian fit to each of the peaks in the TREF or CRYSTAFcurve and integrating the area under each peak wherein the integralunder the entire curve is normalized to 100%.

As used herein, the T₉₀, T₇₅, T₂₅, values represent the temperatures atwhich 90%, 75% and 25%, respectively, of the polymer elutes in a TREFexperiment as described herein.

As used herein, the high density fraction (% high density) is calculatedfrom the integral under the peak that elutes at the higher temperaturein the TREF or CRYSTAF wherein the integral under the entire curve isnormalized to 100%.

As used herein, the non-crystallizing (% non-crystallizing) fraction isindicated by a stepwise increase in the trace below 30° C. in a CRYSTAFexperiment. The non-crystallizing fraction is calculated by integratingthe area of the low temperature side under the CRYSTAF curve wherein theintegral under the entire curve is normalized to 100%.

As used herein, density is measured by the gradient technique accordingto ASTM D 1505.

As used herein, melt index is measured according to ASTM-D-1238-E (190°C., 2.16 kg weight).

As used herein, “substantially” in the phrase “without substantiallychanging the copolymer's density” means that the density change (+/−) isless than 0.015 g/cm³ in some embodiments, less than 0.008 g/cm³ inother embodiments and less than 0.004 g/cm³ in yet other embodiments.

As used herein, “substantially” in the phrase “without substantiallychanging the copolymer's density or melt index” means that the densitychange (+/−) is less than 0.015 g/cm³ in some embodiments, less than0.008 g/cm³ in other embodiments and less than 0.004 g/cm³ in yet otherembodiments, and that the melt index change (+/−) is less than 2 g/10min in some embodiments, less than 1 g/10 min in other embodiments andless than 0.5 g/10 min in yet other embodiments.

As used herein, TREF is measured using an analytical size TREFinstrument (available from Polymerchar, Spain), with a column of thefollowing dimensions: inner diameter (ID) 7.8 mm, outer diameter (OD)9.52 mm, and a column length of 15 cm. The column is filled with steelbeads. 0.5 mL of a 6.4% (w/v) polymer solution in orthodichlorobenzene(ODCB) (ODCB, Aldrich 99+% stabilized with 0.5 g BHT/4 L) containing 6 gBHT/4 L (2,6-Di-tert-butyl-4-methylphenol) is charged onto the columnand cooled from 140° C. to 25° C. at a constant cooling rate of 1.0°C./min. Subsequently, the ODCB is pumped through the column at a flowrate of 1.0 ml/min, and the column temperature is increased at aconstant heating rate of 2° C./min to elute the polymer. The polymerconcentration in the eluted liquid is detected by means of measuring theabsorption at a wave number of 2857 cm⁻¹ using an infrared detector. Theconcentration of the polymer in the solution is then calculated from theabsorption and plotted as a function of temperature.

As used herein, CRYSTAF is measured using a commercial instrument byPolymerChar S.A., Model No. 200. Approximately 20-30 mg of polymer areplaced in a reactor and dissolved in 30 mL 1,2 dichlorobenzene (ODCB,Aldrich 99+% stabilized with 0.5 g BHT/4 L) at 160° C. for 60 minutesfollowed by 45 minutes equilibration time at 100° C. The polymersolutions are cooled to 0° C. using a crystallization rate of 0.2°C./min. A two wavelength infrared detector is used to measure thepolymer concentration during crystallization (3.5 μm, 2853 cm⁻¹ sym.stretch) and to compensate for base line drifts (3.6 μm) during theanalysis time. The solution concentration is monitored at certaintemperature intervals, yielding a cumulative concentration curve. Thederivative of this curve with respect to temperature (dw/dT) representsthe weight fraction of crystallized polymer at each temperature. Thisderivative of the cumulative concentration curve then plotted as afunction of the crystallization temperature.

Catalyst Components

The catalyst system comprises any desirable catalyst composition knownin the art useful in polymerizing olefins such as, but not limited to,vanadium based catalysts, titanium based Ziegler-Natta catalysts (whichmay include a magnesium component), metallocenes, such as Group 4metallocenes (preferably, hafnocenes and zirconocenes), chromium andchromium oxide based catalyst compositions, and Group 3-10coordination-type catalysts systems (e.g., bidentate or tridentateamine/imine coordination complexes with iron, palladium, nickel orzirconium). As used herein, the International Union of Pure and AppliedChemistry (IUPAC) notation (3 Oct. 2005)(www.iupac.org/reports/periodictable/) of the periodic table will bereferenced unless otherwise specified.

In a class of embodiments, the polymerization catalyst comprises ametallocene; in a preferred embodiment, the catalyst compositioncomprises a hafnocene; in a most preferred embodiment, the metalloceneof the catalyst composition consists essentially of a hafnocene, i.e.,one metal complex of hafnium and at least one ligand.

The “hafnocene” may be a catalyst component comprising mono-, bis- ortris-cyclopentadienyl-type complexes of hafnium. In an embodiment, thecyclopentadienyl-type ligand comprises cyclopentadienyl or ligandsisolobal to cyclopentadienyl and substituted versions thereof.Representative examples, but not exclusive, of ligands isolobal tocyclopentadienyl include cyclopentaphenanthreneyl, indenyl, benzindenyl,fluorenyl, octahydrofluorenyl, cyclooctatetraenyl,cyclopentacyclododecene, phenanthrindenyl, 3,4-benzofluorenyl,9-phenylfluorenyl, 8-H-cyclopent[a]acenaphthylenyl, 7H-dibenzofluorenyl,indeno[1,2-9]anthrene, thiophenoindenyl, thiophenofluorenyl,hydrogenated versions thereof (e.g., 4,5,6,7-tetrahydroindenyl, or“H₄Ind”) and substituted versions thereof. In one embodiment, thehafnocene is an unbridged bis-cyclopentadienyl hafnocene and substitutedversions thereof. In another embodiment, the hafnocene excludesunsubstituted bridged and unbridged bis-cyclopentadienyl hafnocenes, andunsubstituted bridged and unbridged bis-indenyl hafnocenes,“unsubstituted” meaning that there are only hydride groups bound to therings and no other group.

Preferably, the hafnocene useful in the present invention can berepresented by the formula (where “Hf” is hafnium):Cp_(n)HfX_(q)  (1)

wherein n is 1 or 2, q is 1, 2 or 3, each Cp is independently acyclopentadienyl ligand or a ligand isolobal to cyclopentadienyl or asubstituted version thereof bound to the hafnium; and X is selected fromthe group consisting of hydride, halides, C₁ to C₁₀ alkyls and C₂ to C₁₂alkenyls; and wherein when n is 2, each Cp may be bound to one anotherthrough a bridging group A selected from the group consisting of C₁ toC₅ alkylenes, oxygen, alkylamine, silyl-hydrocarbons, andsiloxyl-hydrocarbons. An example of C₁ to C₅ alkylenes include ethylene(—CH₂CH₂—) bridge groups; an example of an alkylamine bridging groupincludes methylamide (—(CH₃)N—); an example of a silyl-hydrocarbonbridging group includes dimethylsilyl (—(CH₃)₂Si—); and an example of asiloxyl-hydrocarbon bridging group includes (—O—(CH₃)₂Si—O—).

In an embodiment of the hafnocene represented in formula (1), n is 2 andq is 1 or 2.

As used herein, the term “substituted” means that the referenced grouppossesses at least one moiety in place of one or more hydrogens in anyposition, the moieties selected from such groups as halogen radicals(esp., F, Cl, Br), hydroxyl groups, carbonyl groups, carboxyl groups,amine groups, phosphine groups, alkoxy groups, phenyl groups, naphthylgroups, C₁ to C₁₀ alkyl groups, C₂ to C₁₀ alkenyl groups, andcombinations thereof. Examples of substituted alkyls and aryls includes,but are not limited to, acyl radicals, alkylamino radicals, alkoxyradicals, aryloxy radicals, alkylthio radicals, dialkylamino radicals,alkoxycarbonyl radicals, aryloxycarbonyl radicals, carbamoyl radicals,alkyl- and dialkyl-carbamoyl radicals, acyloxy radicals, acylaminoradicals, arylamino radicals, and combinations thereof.

In another class of embodiments, the hafnocene useful in the presentinvention can be represented by the formula:(CpR₅)₂HfX₂  (2)wherein each Cp is a cyclopentadienyl ligand and each is bound to thehafnium; each R is independently selected from hydrides and C₁ to C₁₀alkyls, most preferably hydrides and C₁ to C₅ alkyls; and X is selectedfrom the group consisting of hydride, halide, C₁ to C₁₀ alkyls and C₂ toC₁₂ alkenyls, and more preferably X is selected from the groupconsisting of halides, C₂ to C₆ alkylenes and C₁ to C₆ alkyls, and mostpreferably X is selected from the group consisting of chloride,fluoride, C₁ to C₅ alkyls and C₂ to C₆ alkylenes. In an embodiment, thehafnocene is represented by formula (2) above, wherein at least one Rgroup is an alkyl as defined above, preferably a C₁ to C₅ alkyl, and theothers are hydrides. In another embodiment, each Cp is independentlysubstituted with from one two three groups selected from the groupconsisting of methyl, ethyl, propyl, butyl, and isomers thereof.

The hafnocene may be selected from the group consisting ofbis(n-propylcyclopentadienyl)hafnium X₂,bis(n-butylcyclopentadienyl)hafnium X₂,bis(n-pentylcyclopentadienyl)hafnium X₂, (n-propylcyclopentadienyl)(n-butylcyclopentadienyl)hafnium X₂,bis[(2-trimethylsilylethyl)cyclopentadienyl]hafnium X₂,bis(trimethylsilyl cyclopentadienyl)hafnium X₂,dimethylsilylbis(n-propylcyclopentadienyl)hafnium X₂,dimethylsilylbis(n-butylcyclopentadienyl)hafnium X₂,bis(1-n-propyl-2-methylcyclopentadienyl)hafnium X₂, and(n-propylcyclopentadienyl)(1-n-propyl-3-n-butylcyclopentadienyl)hafniumX₂, wherein X is selected from the group consisting of halogen ions,hydrides, C1-12 alkyls, C2-12 alkenyls, C6-12 aryls, C7-20 alkylaryls,C1-12 alkoxys, C6-16 aryloxys, C7-18 alkylaryloxys, C1-12 fluoroalkyls,C6-12 fluoroaryls, and C1-12 heteroatom-containing hydrocarbons andsubstituted derivatives thereof.

In certain embodiments, the polymerization process may be carried outsuch that the catalyst composition is heterogeneous and the catalystcomposition comprises at least one support material. The supportmaterial may be any material known in the art for supporting catalystcompositions, such as an inorganic oxide, preferably silica, alumina,silica-alumina, magnesium chloride, graphite, magnesite, titania,zirconia, and montmorillonite, any of which can be chemically/physicallymodified such as by fluoriding processes, calcining, or other processesknown in the art.

In an embodiment, the support material may be a silica material havingan average particle size as determined by Malvern analysis of from 0.1to 100 μm, most preferably 10 to 50 μm.

In a class of embodiments, the catalyst composition may comprises atleast one activator. Such activators are well known in the art andinclude but are not limited to Lewis acids such as cyclic or oligomericpoly(hydrocarbylaluminum oxides and so called non-coordinatingactivators (“NCA”).

The at least one activator may also comprise an alumoxane (e.g.,methylalumoxane “MAO”) and modified alumoxane (e.g., “MMAO” or “TIBAO”).The activators are widely used and known in the art and may be suitableto activate catalyst for olefin polymerization.

In a preferred embodiment, the activator is an alumoxane, and mostpreferably methalumoxane such as described by J. B. P. Soares and A. E.Hamielec in 3(2) POLYMER REACTION ENGINEERING 131-200 (1995). Thealumoxane may be co-supported on the support material, optionally, in amolar ratio of aluminum to hafnium (Al:Hf) ranging from 50:1 to 200:1,or 80:1 to 120:1.

Polymerization Process

The “polymerization reactor” may be any type of reactor known in the artthat is useful in producing polyolefins. An example of such reactor is acontinuous gas phase reactor, more particularly, a continuous fluidizedbed gas phase reactor.

Such reactors, for example, are generally capable of being operated atan overall pressure of less than 10,000 kPa, preferably less than 8,000kPa, and even more preferably less than 6,000 kPa, and even morepreferably less than 4,000 kPa, and most preferably less than 3,000 kPa.

In a class of embodiments, the reactor is a “continuous” reactor,meaning that monomers and catalyst composition are continually orregularly fed to the reactor while the polymer product, for example,polyethylene is continually or regularly extracted from the reactor.Such polymerization reactors include so called “slurry” reactors,“solution” reactors, and “fluidized bed gas phase” reactors. Suchreactors are outlined by A. E. Hamielec and J. B. P. Soares inPolymerization Reaction Engineering—Metallocene Catalysts, 21 PROG.POLYM. SCI. 651-706 (1996).

In a special class of embodiments, the polymerization reactor useful inthe invention is a continuous fluidized bed gas phase reactor comprisinga feed stream or “cycle gas” comprising the ethylene and a comonomer,for example, hexene, butene, octene, and/or mixtures thereof, both ofwhich are flowed continuously through the polymerization reactor by anysuitable means. Such reactors are well known in the art and described inmore detail in U.S. Pat. Nos. 5,352,749, 5,462,999, and WO 03/044061.The amount of comonomer can be expressed as a molar ratio relative tothe amount of ethylene in the reactor. Preferably, the feed stream or“cycle gas” is provided to assist the reactor in maintaining acontinuous flow of ethylene and comonomer.

In embodiments utilizing the fluidized bed gas phase reactor, a monomerstream is passed to a polymerization section. As an illustration of thepolymerization section, there can be included a reactor in fluidcommunication with one or more discharge tanks, surge tanks, purgetanks, and recycle compressors. In one or more embodiments, the reactorincludes a reaction zone in fluid communication with a velocityreduction zone. The reaction zone includes a bed of growing polymerparticles, formed polymer particles and catalyst composition particlesfluidized by the continuous flow of polymerizable and modifying gaseouscomponents in the form of make-up feed and recycle fluid through thereaction zone. Preferably, the make-up feed includes polymerizablemonomer, most preferably ethylene and at least one other α-olefin, andmay also include “condensing agents” as is known in the art anddisclosed in, for example, U.S. Pat. Nos. 4,543,399, 5,405,922, and5,462,999.

The fluidized bed has the general appearance of a dense mass ofindividually moving particles, preferably polyethylene particles, ascreated by the percolation of gas through the bed. The pressure dropthrough the bed may be equal to or slightly greater than the weight ofthe bed divided by the cross-sectional area. It is thus dependent on thegeometry of the reactor. To maintain a viable fluidized bed in thereaction zone, the superficial gas velocity through the bed must exceedthe minimum flow required for fluidization. Preferably, the superficialgas velocity may be at least two times the minimum flow velocity.

In general, the height to diameter ratio of the reaction zone may varyin the range of about 2:1 to about 5:1. The range, of course, can varyto larger or smaller ratios and depends upon the desired productioncapacity. The cross-sectional area of the velocity reduction zone istypically within the range of about 2 to about 3 multiplied by thecross-sectional area of the reaction zone.

The velocity reduction zone has a larger inner diameter than thereaction zone, and can be conically tapered in shape. As the namesuggests, the velocity reduction zone slows the velocity of the gas dueto the increased cross sectional area. This reduction in gas velocitydrops the entrained particles into the bed, reducing the quantity ofentrained particles that flow from the reactor. That gas exiting theoverhead of the reactor is the recycle gas stream.

The recycle stream is compressed in a compressor and then passed througha heat exchange zone where heat is removed before it is returned to thebed. The heat exchange zone is typically a heat exchanger which can beof the horizontal or vertical type. If desired, several heat exchangerscan be employed to lower the temperature of the cycle gas stream instages. It is also possible to locate the compressor downstream from theheat exchanger or at an intermediate point between several heatexchangers. After cooling, the recycle stream is returned to the reactorthrough a recycle inlet line. The cooled recycle stream absorbs the heatof reaction generated by the polymerization reaction.

Typically, the recycle stream is returned to the reactor and to thefluidized bed through a gas distributor plate. A gas deflector ispreferably installed at the inlet to the reactor to prevent containedpolymer particles from settling out and agglomerating into a solid massand to prevent liquid accumulation at the bottom of the reactor as wellto facilitate easy transitions between processes which contain liquid inthe cycle gas stream and those which do not and vice versa. Anillustrative deflector suitable for this purpose is described in, forexample, U.S. Pat. Nos. 4,933,149 and 6,627,713.

The catalyst composition or system used in the fluidized bed ispreferably stored for service in a reservoir under a blanket of a gaswhich is inert (or does not react during the polymerization process) tothe stored material, such as nitrogen or argon. The catalyst compositionmay be added to the reaction system, or reactor, at any point and by anysuitable means, and is preferably added to the reaction system eitherdirectly into the fluidized bed or downstream of the last heat exchanger(the exchanger farthest downstream relative to the flow) in the recycleline, in which case the activator is fed into the bed or recycle linefrom a dispenser. The catalyst composition is injected into the bed at apoint above distributor plate. Preferably, the catalyst composition isinjected at a point in the bed where good mixing with polymer particlesoccurs. Injecting the catalyst composition at a point above thedistribution plate provides satisfactory operation of a fluidized bedpolymerization reactor.

The monomers can be introduced into the polymerization zone in variousways including direct injection through a nozzle into the bed or cyclegas line. The monomers can also be sprayed onto the top of the bedthrough a nozzle positioned above the bed, which may aid in eliminatingsome carryover of fines by the cycle gas stream.

Make-up fluid may be fed to the bed through a separate line to thereactor. The composition of the make-up stream is determined by a gasanalyzer. The gas analyzer determines the composition of the recyclestream and the composition of the make-up stream is adjusted accordinglyto maintain an essentially steady state gaseous composition within thereaction zone. The gas analyzer can be a conventional gas analyzer thatdetermines the recycle stream composition to maintain the ratios of feedstream components. Such equipment is commercially available from a widevariety of sources. The gas analyzer is typically positioned to receivegas from a sampling point located between the velocity reduction zoneand heat exchanger.

The production rate of polyolefin may be conveniently controlled byadjusting the rate of catalyst composition injection, activatorinjection, or both. Since any change in the rate of catalyst compositioninjection will change the reaction rate and thus the rate at which heatis generated in the bed, the temperature of the recycle stream enteringthe reactor is adjusted to accommodate any change in the rate of heatgeneration. This ensures the maintenance of an essentially constanttemperature in the bed. Complete instrumentation of both the fluidizedbed and the recycle stream cooling system is, of course, useful todetect any temperature change in the bed so as to enable either theoperator or a conventional automatic control system to make a suitableadjustment in the temperature of the recycle stream.

Under a given set of operating conditions, the fluidized bed ismaintained at essentially a constant height by withdrawing a portion ofthe bed as product at the rate of formation of the particulate polymerproduct. Since the rate of heat generation is directly related to therate of product formation, a measurement of the temperature rise of thefluid across the reactor (the difference between inlet fluid temperatureand exit fluid temperature) is indicative of the rate of particularpolymer formation at a constant fluid velocity if no or negligiblevaporizable liquid is present in the inlet fluid.

On discharge of particulate polymer product from reactor, it isdesirable and preferable to separate fluid from the product and toreturn the fluid to the recycle line. There are numerous ways known tothe art to accomplish this separation. Product discharge systems whichmay be alternatively employed are disclosed and claimed in U.S. Pat. No.4,621,952. Such a system typically employs at least one (parallel) pairof tanks comprising a settling tank and a transfer tank arranged inseries and having the separated gas phase returned from the top of thesettling tank to a point in the reactor near the top of the fluidizedbed.

In order to maintain an adequate reactor operability and catalystproductivity, it is preferable that the reactor temperature of thefluidized bed in the fluidized bed gas-phase reactor embodiment hereinranges from 70° C. or 75° C. or 80° C. to 90° C. or 95° C. or 100° C. or110° C., wherein a desirable temperature range comprises any uppertemperature limit combined with any lower temperature limit describedherein. In addition to using the reactor temperature as a means tomaintain reactor operability and catalyst productivity, the presentinvention provides for a method to use the reactor temperature, amongother variables, to alter the composition distribution of thepolyolefin.

In a class of embodiment, in order to maintain an adequate catalystproductivity in the present invention, it is preferable that theethylene is present in the reactor at a partial pressure at or greaterthan 100 psia (690 kPa), or 120 psia (830 kPa), or 190 psia (1300 kPa),or 200 psia (1380 kPa), or 210 psia (1450 kPa), or 220 psia (1515 kPa);and less than 10,000 kPa in a preferred embodiment. In addition to usingthe partial pressure of ethylene as a means to maintain catalystproductivity, the present invention provides for a method to use thepartial pressure of ethylene, among other variables, to alter thecomposition distribution of the polyolefin.

In certain embodiments, the process of the invention is characterized inthat when the ethylene partial pressure is changed by at least 50 kPa orthe reactor temperature is changed by at least 1° C. or both, thecomposition distribution of the produced polyethylene changes. Thischange in composition distribution may be characterized by one or moreof the following:

-   -   a) the composition distribution changes such that the T₇₅-T₂₅        value changes by at least 5° C. or the T₉₀ value changes by at        least 5° C.;    -   b) the area under the high temperature peak in a TREF or CRYSTAF        experiment increases or decreases by at least 5%;    -   c) the fraction of non-crystallizing polymer chains changes by        at least 5%, wherein the fraction of non-crystallizing polymer        chains is indicated by a stepwise increase in the trace below        30° C. in a CRYSTAF experiment;    -   d) a decrease of one peak in a TREF or a CRYSTAF experiment of a        polyethylene having a bimodal composition distribution such that        a unimodal composition distribution results; and    -   e) the appearance of an additional peak in a TREF or a CRYSTAF        experiment of a polyethylene having a unimodal composition        distribution such that a bimodal composition distribution        results.

The molar ratio of copolymer to ethylene may be used to control thedensity of the resultant ethylene alpha-olefin copolymer, where highermolar ratios of copolymer to ethylene produce lower densitypolyethylenes. The final polyethylene product may comprise from 0 to 15or 20 wt % comonomer derived units. Preferably, ethylene iscopolymerized with α-olefins containing from 3 to 12 carbon atoms in oneembodiment, and from 4 to 10 carbon atoms in yet another embodiment, andfrom 4 to 8 carbon atoms in a preferable embodiment. In severalembodiments, ethylene is copolymerized with 1-butene or 1-hexene.

The comonomer is present at any level that will achieve the desiredweight percent incorporation of the comonomer into the finishedpolyethylene, and thus a desired density. The molar ratio of comonomerto ethylene as described herein, is the ratio of the gas concentrationof comonomer moles in the cycle gas to the gas concentration of ethylenemoles in the cycle gas. In one embodiment, the comonomer is present withethylene in the cycle gas in a mole ratio range of from 0.0001(comonomer:ethylene) to 0.20 or 0.10, and from 0.001 to 0.1 in anotherembodiment, and from 0.001 to 0.050 in yet another embodiment, and from0.002 to 0.030 in yet another embodiment, wherein a desirable range maycomprise any combination of any upper limit with any lower limit asdescribed herein. In addition to providing a means for controlling basicproperties of the produced polyolefin such as I₂₁ and/or I₂ and bulkdensity, the present invention provides for a method to use thecomonomer to ethylene ratio, among other variables, to alter thecomposition distribution of the polyolefin.

Hydrogen gas may also be added to the polymerization reactor to achievea desired melt index, such as I₂ or I₂₁. In one embodiment, the ratio ofhydrogen to total ethylene monomer (ppm H₂: mol % C₂) in the circulatinggas stream is in a range of from 0 to 60:1 in one embodiment, and from0.10:1 (0.10) to 50:1 (50) in another embodiment, and from 0.12 to 40 inyet another embodiment, and from 0.15 to 35 in yet another embodiment,wherein a desirable range may comprise any combination of any upper moleratio limit with any lower mole ratio limit described herein. Inaddition to providing a means for controlling basic properties of theproduced polyolefin such as I₂₁ and/or I₂ and bulk density, the presentinvention provides for a method to use the hydrogen to ethylene ratio,among other variables, to alter the composition distribution of thepolyolefin.

In certain embodiments, the process of the invention is characterized inthat when the hydrogen to ethylene ratio in the reactor or the comonomerto ethylene ratio in the reactor or both is changed by at least 5%, thecomposition distribution of the produced polyethylene changes. Thischange in composition distribution may be characterized by one or moreof the following:

-   -   a) the composition distribution changes such that the T₇₅-T₂₅        value changes by at least 5° C. or the T₉₀ value changes by at        least 5° C.;    -   b) the area under the high temperature peak in a TREF or CRYSTAF        experiment increases or decreases by at least 5%;    -   c) the fraction of non-crystallizing polymer chains changes by        at least 5%, wherein the fraction of non-crystallizing polymer        chains is indicated by a stepwise increase in the trace below        30° C. in a CRYSTAF experiment;    -   d) a decrease of one peak in a TREF or a CRYSTAF experiment of a        polyethylene having a bimodal composition distribution such that        a unimodal composition distribution results; and    -   e) the appearance of an additional peak in a TREF or a CRYSTAF        experiment of a polyethylene having a unimodal composition        distribution such that a bimodal composition distribution        results;

Polymer

The present invention is suitable for forming a broad range ofpolyethylene copolymers. In one embodiment, the polyethylene producedfrom the process of the invention has a melt index (I₂ as measuredaccording to ASTM-D-1238-E 190° C./2.16 kg) of from 0.01 to 200 dg/min.Further, the polyethylene may have an I₂₁/I₂ (I₂₁ as measured byASTM-D-1238-F, 190° C./21.6 kg) value of from 10 to 100 in oneembodiment, and from 10 to 50 in yet another embodiment, and from 12 to40 in yet another embodiment, and from 15 to 35 in yet anotherembodiment.

The density of the polyethylenes described herein may range from 0.910to 0.975 g/cm³ preferably form 0.910 to 0.965 g/cm³ more preferably form0.910 to 0.960 g/cm³ as measured by ASTM D 792.

The polyethylene preferably may have a molecular weight distribution offrom 2 to 15 in one embodiment, and from 2 to 10 in another embodiment,and from 2.5 to 8 in yet another embodiment, and from 2.5 to 5 in yetanother embodiment, wherein a desirable range may comprise anycombination of any upper limit with any lower limit described herein.

The polyethylene may have a hexane extractables value (as measured by 21CFR 177.1520(d)(3)(i)) of less than 2% in one embodiment, and less than1% in another embodiments.

In certain embodiments, the polyethylene has substantially no chromium,zirconium, vanadium or titanium content, that is only amounts that wouldbe considered by those skilled in the art trace amounts of these metals,such as, for example, less than 0.01 ppm. In other embodiments, thepolyethylene comprises from 0.001 to 4 ppm of hafnium, and morepreferably between 0.001 and 3 ppm of hafnium. The metals content may bedetermined by X-ray fluorescence analysis (XRF) or Inductively CoupledPlasma-Atomic Emission Spectrometry (ICP-AES), as is known in the art.

The polyethylene can be formed into any useful article of manufacture byany suitable means. The polyethylenes of the invention are well suitedfor films made by the cast or blown film extrusion processes. Thepolyethylenes of the invention are particularly well suited for beingformed into an article by a rotational molding or injection moldingprocess. Such processes are well known in the art. Typical rotationalmolded articles include large containers for conveying liquids, drums,agricultural tanks, and large parts such as canoes or large playgroundtoys. Typical injection molded articles include, housewares, thin wallcontainers, and lids for containers.

It is contemplated by the inventors that the polyethylene of the presentinvention may be blended with other polymers and/or additives to formcompositions that can be used in articles of manufacture. The blends maybe formed into such articles of manufacture by cast film extrusion,blown film extrusion, rotational molding or injection molding processes.

In a class of embodiments and in one aspect of the invention, topolymerize ethylene and one or more alpha-olefins with a catalyst systemin a polymerization reactor, wherein the composition distribution may bealtered by changing one or more of the following: the molar ratio ofcomonomer to ethylene, the molar ratio of hydrogen to ethylene or thepartial pressure of ethylene and the reactor temperature. Preferably,the polymerization reactor is a single continuous gas phase reactoroperating at less than 10,000 kPa pressure and the catalyst systemcomprises a single metallocene catalyst such as described herein.Preferably, the single metallocene system a hafnocene.

EXAMPLES

It is to be understood that while the invention has been described inconjunction with the specific embodiments thereof, the foregoingdescription is intended to illustrate and not limit the scope of theinvention. Other aspects, advantages and modifications will be apparentto those skilled in the art to which the invention pertains.

Therefore, the following examples are put forth so as to provide thoseskilled in the art with a complete disclosure and description of how tomake and use the compounds of the invention, and are not intended tolimit the scope of that which the inventors regard as their invention.

Examples 1-8

Ethylene/1-hexene copolymers were produced according to the followingprocedure. The catalyst composition comprised a silica supportedbis(n-propylcyclopentadienyl)hafnium dichloride with methalumoxane, theAl:Hf ratio being from about 80:1 to 130:1. Methods of preparing thecatalyst composition are disclosed in, for example U.S. Pat. No.6,242,545. The catalyst composition was injected dry into a fluidizedbed gas phase polymerization reactor. More particularly, polymerizationwas conducted in a 152.4 mm diameter gas-phase fluidized bed reactoroperating at approximately 2068 kPa total pressure. The reactor bedweight was approximately 2 kg. Fluidizing gas was passed through the bedat a velocity of approximately 0.6 m per second. The fluidizing gasexiting the bed entered a resin disengaging zone located at the upperportion of the reactor. The fluidizing gas then entered a recycle loopand passed through a cycle gas compressor and water-cooled heatexchanger. The shell side water temperature was adjusted to maintain thereactor temperature as specified in Tables 1 and 2. Ethylene, hydrogen,1-hexene and nitrogen were fed to the cycle gas loop just upstream ofthe compressor at quantities sufficient to maintain the desired gasconcentrations as specified in Tables 1 and 2. Gas concentrations weremeasured by an on-line vapor fraction analyzer. Product (polyethyleneparticles) was withdrawn from the reactor in batch mode into a purgingvessel before it was transferred into a product bin. Residual catalystand activator in the resin was deactivated in the product drum with awet nitrogen purge. The catalyst was fed to the reactor bed through astainless steel injection tube at a rate sufficient to maintain thedesired polymer production rate. “C₆/C₂ flow ratio (“FR”)” is the ratioof the lbs of 1-hexene comonomer feed to the pounds of ethylene feed tothe reactor, whereas the C₆/C₂ ratio is the ratio of the gasconcentration of 1-hexene moles in the cycle gas to the gasconcentration of ethylene moles in the cycle gas. The C₆/C₂ ratio isobtained from a cycle gas vapor fraction analyzer, whereas the C₆/C₂Flow Ratio comes from some measure of the mass flow. The cycle gas isthe gas in the reactor, and is measured from a tap off the recirculatingloop around the reactor. The ratios reported in the following tables(Tables 1-4) are from the gas concentrations in the reactor. Samples aretaken every 9 min, and thus reported C₆/C₂ ratios are running averages.Tables 1 and 2 summarize the respective gas concentrations and reactorvariables as well as densities and melt indices of the producedpolymers.

Examples 9-13

The ethylene/1-hexene copolymers were produced in a continuous gas phasefluidized bed reactor similar to the one used in Examples 1-8, exceptthe diameter is 14 inches (355.6 mm), with varying reactor temperatureand partial pressure of ethylene. The catalyst composition comprisedsilica supported bis(n-propylcyclopentadienyl)hafnium dichloride withmethalumoxane, the Al:Hf ratio being from about 80:1 to 130:1. Table 3summarizes the respective gas concentrations and reactor variables aswell as density and melt index of the produced polymers.

Table 1 is directed to gas phase polymerizations of ethylene and1-hexene with the bis-(n-propylcyclopentadienyl)hafnium dichloridecatalyst where the amounts of comonomer and hydrogen are varied in thereactor while maintaining a density range from about 0.922 g/cm³ toabout 0.926 g/cm³. The melt index was measured according toASTM-D-1238-E (190° C., 2.16 kg weight). The density was measuredaccording to ASTM D 792. T₉₀, T₇₅ and T₂₅ were measure as describedherein.

TABLE 1 Example -001 -002 -003 -004 Process data Molar H2/C2 ratio8.7E−4 4.6E−4 4.6E−4 0.14E−4 Molar C6/C2ratio 0.013 0.011 0.009 0.005 C2partial pressure 130 130 130 130 (psi) RX pressure (psig) 300 300 300300 H2 conc. mol ppm 296 162 162 49 H2 flow/sccm 8.3 4.66 5.8 0 C6 conc.(mol %) 0.44 0.37 0.31 0.17 C2 conc. (mol %) 33.9 34.9 35 35.1 C6/C2flow ratio 0.071 0.059 0.047 0.022 C2flow (g/hr) 390 478 551 551 ReactorTemp (° C.) 79.5 79.5 79.5 79.5 Production g 337 404 469 431(polymer)/hr Residence time (hr) 5.6 4.7 4.1 4.4 Avg velocity (ft/s)1.55 1.58 1.57 1.58 Resin Properties T₉₀ 94.2 95.2 96 97.5 T₇₅-T₂₅ 15.111.8 9.1 2.2 Melt Index (dg/min) 10.7 1.4 1.8 0.15 Density (g/cm³)0.9237 0.9219 0.9255 0.9244

The polymers described in Examples 1-4 have similar densities of betweenabout 0.922 g/cm³ and about 0.926 g/cm³ but different compositiondistributions. The composition distributions changed as a result of thevarying comonomer/ethylene and hydrogen/ethylene ratios at constantreactor pressure and temperature. Table 1 summarizes the respective gasconcentrations and reactor variables as well as density and melt indexof the produced polymers of examples 1-4. The T₇₅-T₂₅ value indicatesthe change in composition distribution.

The effect of the comonomer/ethylene and hydrogen/ethylene ratios on thecomposition distributed is demonstrated in FIG. 1. As shown, as thecomonomer/ethylene ratio increases, the composition distributionbroadens. Since an increase in the comonomer/ethylene ratio wouldtypically lower the density, hydrogen was added to the reactor to offsetthe density lowering effect of the increased comonomer concentration.The broadening of the composition distributed is further indicated by anincrease in the T₇₅−T₂₅ value with increasing comonomer concentration.

Examples 2 and 3 demonstrate how changes in the comonomer/ethylene ratioaffect the breadth of the composition distribution as well as themodality of the composition distribution in the resulting polymers. Anincrease in the comonomer/ethylene ratio at constant hydrogenconcentration can be used to broaden the composition distribution. TheTREF curves are shown in FIG. 1.

Examples 2 and 3 further demonstrate that an increase in thecomonomer/ethylene ratio at constant hydrogen concentration can be usedto change a monomodal composition distribution to a bimodal compositiondistribution. The composition distributions (TREF curves) are shown inFIG. 1.

Table 2 is directed to gas phase polymerizations of ethylene and1-hexene with the bis-(n-propylcyclopentadienyl)hafnium dichloridecatalyst where the amounts of comonomer and hydrogen in the reactor arevaried while maintaining a density from about 0.914 g/cm³ to about 0.917g/cm³. The melt index was measured according to ASTM-D-1238-E (190° C.,2.16 kg weight). The density was measured according to ASTM D 792. T₉₀,T₇₅ and T₂₅ were measure as described herein.

TABLE 2 Example -005 -006 -007 -008 Process data Molar H2/C2 ratio1.7E−4 5.3E−4 13.3E−4 33.1E−4 Molar C6/C2ratio 0.012 0.013 0.016 0.015C2 partial pressure 130 130 130 130 (psi) RX pressure (psig) 300 300 300300 Reactor Temp (° C.) 75 75 80 80 H2 conc. mol ppm 59 184 465 1161 H2flow/sccm 0 5.18 14.6 36.99 C6 conc. (mol %) 0.42 0.47 0.56 0.52 C2conc. (mol %) 35 35 35 35 C6/C2 flow ratio 0.073 0.089 0.131 0.14 C2flow(g/hr) 614 511 536 545 Production g 487 431 460 47 5 (polymer)/hrResidence time (hr) 3.9 4.3 4.1 4 Avg velocity (ft/s) 1.6 1.6 1.59 1.57Resin Properties T₉₀ 95.4 94.7 88.4 81.5 T₇₅-T₂₅ 11 22.5 18.9 19.9 %high density 50.6 35.9 9.3 3.8 Melt Index (dg/min) 0.077 1.08 9.4 158Density (g/cm³) 0.9144 0.9172 0.9155 0.9164

The polymers described in Examples 5-8 have similar densities of betweenabout 0.914 g/cm³ and about 0.917 g/cm³ but different compositiondistributions. The composition distributions changed as a result of thevarying comonomer/ethylene and hydrogen/ethylene ratios at constantreactor pressure. Tables 2 summarize the respective gas concentrationsand reactor variables as well as density and melt index of the producedpolymers of examples 5-8.

The effect of the comonomer/ethylene and hydrogen/ethylene ratios on thecomposition distributed is demonstrated in FIG. 2. As shown, as thehydrogen/ethylene ratio increases, the composition distribution broadensand the relative amounts of high and low temperature peaks change. Thischange is characterized in that the low temperature peak in the TREFcurve increases in contrast to the high temperature peak and also by adecrease in % high density.

Table 3 is directed to gas phase polymerizations of ethylene and1-hexene with the bis-(n-propylcyclopentadienyl)hafnium dichloridecatalyst where the ethylene partial pressure and reactor temperature arevaried while maintaining a constant C₆/C₂ ratio and a constant hydrogenconcentration in the reactor. The melt index was measured according toASTM-D-1238-E (190° C., 2.16 kg weight). The density was measuredaccording to ASTM D 792.

TABLE 3 Example 9 10 11 12 13 Process data: Reactor Temperature 85 75 7590 90 (° C.) Reactor Pressure (psi) 350 350 350 350 350 C2PP (psi) 220180 240 240 180 Recycle Gas Velocity 1.9 1.9 1.9 1.9 1.9 (ft./sec) H2/C2Molar Ratio 6.5E−4 6.5E−4 6.5E−4 6.5E−5 6.5E−4 C6/C2 Molar Ratio 0.0170.017 0.017 0.017 0.017 Residence Time (hr.) 2.9 2.7 3.1 3.5 3.0 BedWeight (lbs.) 110 110 110 110 110 Productivity (g 3624 3728 4200 30992628 polymer/g catalyst) Resin Properties: Melt Index (dg/min) 0.65 0.700.90 0.35 0.32 Density (g/cc) 0.917 0.916 0.923 0.915 0.910 % highdensity 60.0 53.3 67.0 57.5 35.0 % non-crystallizing 2.6 14.3 11.1 1.40.8

The polymers described in Examples 9-13 were produced with varyingethylene partial pressures and reactor temperatures while maintainingconstant C₆/C₂ ratios and constant hydrogen concentrations.

FIG. 3 shows the CRYSTAF curves of examples 12 and 13 to demonstrate theeffect of ethylene partial pressure on the composition distribution:Example 13 was produced with higher ethylene partial pressure (240 psi).It exhibits a relatively strong high temperature peak compared to thelow temperature peak. Example 12 was produced at lower ethylene partialpressure of 180 psi while keeping all other variables substantiallyconstant. Compared to Example 13, Example 12 shows a weaker hightemperature peak and a stronger low temperature peak.

FIG. 4 shows the CRYSTAF curves of Examples 11 and 12 and demonstratesthe effect of reactor temperature on the composition distribution of theproduced polymer. Examples 11 and 12 were produced under similarconditions, except Examples 11 was produced at a lower reactortemperature. The polymer produced at higher reactor temperature shows abimodal composition distribution. A lower reactor temperaturesignificantly increases the fraction of high density polymer (% highdensity) and the composition distribution of the lower reactortemperature polymer is further altered in that the peak at lowercrystallization temperature decreases and thus a monomodal compositiondistribution results. Furthermore, a lower reactor temperature increasesthe fraction of non-crystallizing polymer chains as evidenced by astepwise increase in the CRYSTAF trace below 30° C.

FIG. 5 shows the CRYSTAF curves of Examples 9 and 10. In FIG. 5, it isshown that two resins having similar densities and melt indices butdifferent composition distributions can be produced by adjusting reactortemperature and ethylene partial pressure. The resin produced at lowerreactor temperature and lower ethylene partial pressure (Example 10)shows a lower high density fraction (% high density) but a greater noncrystallizing fraction.

As stated above, it would be desirable to control the compositiondistribution of an ethylene alpha-olefin copolymer and producepolyethylene resins without having to change the catalyst compositionand without having to use multiple reactors. In various embodimentsdescribed herein, the invention provides for at least one of utilizinghydrogen concentration, the ratio of comonomer to ethylene, reactortemperature, and ethylene partial pressure in combination with thecatalyst system to tailor at least one of melt index, density, andcomposition distribution of the polymer product such as polyethylene.

The phrases, unless otherwise specified, “consists essentially of” and“consisting essentially of” do not exclude the presence of other steps,elements, or materials, whether or not, specifically mentioned in thisspecification, as along as such steps, elements, or materials, do notaffect the basic and novel characteristics of the invention,additionally, they do not exclude impurities normally associated withthe elements and materials used.

For the sake of brevity, only certain ranges are explicitly disclosedherein. However, ranges from any lower limit may be combined with anyupper limit to recite a range not explicitly recited, as well as, rangesfrom any lower limit may be combined with any other lower limit torecite a range not explicitly recited, in the same way, ranges from anyupper limit may be combined with any other upper limit to recite a rangenot explicitly recited. Additionally, within a range includes everypoint or individual value between its end points even though notexplicitly recited. Thus, every point or individual value may serve asits own lower or upper limit combined with any other point or individualvalue or any other lower or upper limit, to recite a range notexplicitly recited.

All priority documents are herein fully incorporated by reference forall jurisdictions in which such incorporation is permitted and to theextent such disclosure is consistent with the description of the presentinvention. Further, all documents and references cited herein, includingtesting procedures, publications, patents, journal articles, etc. areherein fully incorporated by reference for all jurisdictions in whichsuch incorporation is permitted and to the extent such disclosure isconsistent with the description of the present invention.

While the invention has been described with respect to a number ofembodiments and examples, those skilled in the art, having benefit ofthis disclosure, will appreciate that other embodiments can be devisedwhich do not depart from the scope and spirit of the invention asdisclosed herein.

1. A method of forming a first and a second ethylene alpha-olefincopolymer, the method comprising contacting a reaction mixture and acatalyst system comprising a hafnocene in a reactor, the reactionmixture comprising ethylene, hydrogen, and one or more alpha olefins,and altering at least one or more of the following: i) the molar ratioof hydrogen to ethylene, ii) the molar ratio of comonomer to ethylene,iii) the ethylene partial pressure and, and iv) the reactor temperature;so that the first ethylene alpha-olefin copolymer has a monomodalcomposition distribution characterized by having a single peak in a TREFexperiment and the second ethylene alpha-olefin copolymer has amultimodal composition distribution characterized by having at least twopeaks in a TREF experiment.
 2. The method of claim 1, wherein thedensities of the first and the second ethylene alpha-olefin copolymerdiffer by no more than 0.015 g/cm³.
 3. The method of claim 1, whereinthe densities of the first and the second ethylene alpha-olefincopolymer differ by no more than 0.008 g/cm³.
 4. The method of claim 1,wherein the densities of the first and the second ethylene alpha-olefincopolymer differ by no more than 0.004 g/cm³.
 5. The method of claim 1,wherein the melt indices of the first and the second ethylenealpha-olefin copolymer differ by no more than 20%.
 6. The method ofclaim 1, wherein the melt indices of the first and the second ethylenealpha-olefin copolymer differ by no more than 10%.
 7. The method ofclaim 1, wherein the hafnocene is selected from the group consisting of:bis(n-propylcyclopentadienyl)hafnium X₂,bis(n-butylcyclopentadienyl)hafnium X₂,bis(n-pentylcyclopentadienyl)hafnium X₂, (n-propylcyclopentadienyl)(n-butylcyclopentadienyl)hafnium X₂,bis[(2-trimethylsilylethyl)cyclopentadienyl]hafnium X₂,bis(trimethylsilyl cyclopentadienyl)hafnium X₂,dimethylsilylbis(n-propylcyclopentadienyl)hafnium X₂,dimethylsilylbis(n-butylcyclopentadienyl)hafnium X₂,bis(1-n-propyl-2-methylcyclopentadienyl)hafnium X₂, and(n-propylcyclopentadienyl)(1-n-propyl-3-n-butylcyclopentadienyl)hafniumX₂; wherein X is selected from the group consisting of halogen ions,hydrides, C1-12 alkyls, C2-12 alkenyls, C6-12 aryls, C7-20 alkylaryls,C1-12 alkoxys, C6-16 aryloxys, C7-18 alkylaryloxys, C1-12 fluoroalkyls,C6-12 fluoroaryls, and C1-12 heteroatom-containing hydrocarbons andsubstituted derivatives thereof.
 8. The method of claim 1, wherein thecatalyst system comprises an activator.
 9. The method of claim 1,wherein the activator comprises an alumoxane.
 10. The method of claim 9,wherein the ratio of Aluminum to Hafnium is from 60:1 to 150:1.
 11. Themethod of claim 9, wherein the ratio of Aluminum to Hafnium is from 80:1to 120:1.
 12. The method of claim 1, wherein the reaction mixturefurther comprises at least one condensing agent that comprises analiphatic hydrocarbon selected from the group consisting of ethane,propane, n-butane, isobutane, n-pentane, isopentane, neopentane,n-hexane, isohexane, heptane, n-octane, and combinations thereof.
 13. Amethod of forming a first and a second ethylene alpha-olefin copolymer,the method comprising contacting a reaction mixture and a catalystsystem comprising a hafnocene in a reactor, the reaction mixturecomprising ethylene, hydrogen, and one or more alpha olefins, andaltering at least one or more of the following: i) the molar ratio ofhydrogen to ethylene, ii) the molar ratio of comonomer to ethylene, iii)the ethylene partial pressure and, iv) the reactor temperature; so thatthe T₉₀ value of the first ethylene alpha-olefin copolymer and thesecond ethylene alpha-olefin copolymer differ by 5° C. or more.
 14. Themethod of claim 13, wherein the densities of the first and the secondethylene alpha-olefin copolymer differ by no more than 0.015 g/cm³. 15.The method of claim 13, wherein the densities of the first and thesecond ethylene alpha-olefin copolymer differ by no more than 0.008g/cm³.
 16. The method of claim 13, wherein the melt indices of the firstand the second ethylene alpha-olefin copolymer differ by no more than20%.
 17. The method of claim 13, wherein the melt indices of the firstand the second ethylene alpha-olefin copolymer differ by no more than10%.
 18. The method of claim 13, wherein the hafnocene is selected fromthe group consisting of: bis(n-propylcyclopentadienyl)hafnium X₂,bis(n-butylcyclopentadienyl)hafnium X₂,bis(n-pentylcyclopentadienyl)hafnium X₂, (n-propylcyclopentadienyl)(n-butylcyclopentadienyl)hafnium X₂,bis[(2-trimethylsilylethyl)cyclopentadienyl]hafnium X₂,bis(trimethylsilyl cyclopentadienyl)hafnium X₂,dimethylsilylbis(n-propylcyclopentadienyl)hafnium X₂,dimethylsilylbis(n-butylcyclopentadienyl)hafnium X₂,bis(1-n-propyl-2-methylcyclopentadienyl)hafnium X₂, and(n-propylcyclopentadienyl)(1-n-propyl-3-n-butylcyclopentadienyl)hafniumX₂; wherein X is selected from the group consisting of halogen ions,hydrides, C1-12 alkyls, C2-12 alkenyls, C6-12 aryls, C7-20 alkylaryls,C1-12 alkoxys, C6-16 aryloxys, C7-18 alkylaryloxys, C1-12 fluoroalkyls,C6-12 fluoroaryls, and C1-12 heteroatom-containing hydrocarbons andsubstituted derivatives thereof.
 19. The method of claim 13, wherein thecatalyst system comprises an activator that comprises an alumoxane. 20.The method of claim 13, wherein the ratio of Aluminum to Hafnium is from60:1 to 150:1.
 21. A method of forming a first and a second ethylenealpha-olefin copolymer, the method comprising contacting a reactionmixture and a catalyst system comprising a hafnocene in a reactor, thereaction mixture comprising ethylene, hydrogen, and one or more alphaolefins, and altering at least one or more of the following: i) themolar ratio of hydrogen to ethylene, ii) the molar ratio of comonomer toethylene, iii) the ethylene partial pressure and, iv) the reactortemperature; so that the T₇₅−T₂₅ value of the first ethylenealpha-olefin copolymer and the second ethylene alpha-olefin copolymerdiffer by 5° C. or more.
 22. The method of claim 21, wherein the T₇₅−T₂₅value of the first ethylene alpha-olefin copolymer and the secondethylene alpha-olefin copolymer differ by 10° C. or more.
 23. The methodof claim 21, wherein the densities of the first and the second ethylenealpha-olefin copolymer differ by no more than 0.015 g/cm³.
 24. Themethod of claim 21, wherein the densities of the first and the secondethylene alpha-olefin copolymer differ by no more than 0.008 g/cm³. 25.The method of claim 21, wherein the melt indices of the first and thesecond ethylene alpha-olefin copolymer differ by no more than 20%. 26.The method of claim 21, wherein the hafnocene is selected from the groupconsisting of: bis(n-propylcyclopentadienyl)hafnium X₂,bis(n-butylcyclopentadienyl)hafnium X₂,bis(n-pentylcyclopentadienyl)hafnium X₂, (n-propylcyclopentadienyl)(n-butylcyclopentadienyl)hafnium X₂,bis[(2-trimethylsilylethyl)cyclopentadienyl]hafnium X₂,bis(trimethylsilyl cyclopentadienyl)hafnium X₂,dimethylsilylbis(n-propylcyclopentadienyl)hafnium X₂,dimethylsilylbis(n-butylcyclopentadienyl)hafnium X₂,bis(1-n-propyl-2-methylcyclopentadienyl)hafnium X₂, and(n-propylcyclopentadienyl)(1-n-propyl-3-n-butylcyclopentadienyl)hafniumX₂; wherein 26 is selected from the group consisting of halogen ions,hydrides, C1-12 alkyls, C2-12 alkenyls, C6-12 aryls, C7-20 alkylaryls,C1-12 alkoxys, C6-16 aryloxys, C7-18 alkylaryloxys, C1-12 fluoroalkyls,C6-12 fluoroaryls, and C1-12 heteroatom-containing hydrocarbons andsubstituted derivatives thereof.